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• • C—CHEMISTRY; METALLURGY
  • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
  • C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
  • C04B35/00—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products
  • C04B35/01—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on oxide ceramics
  • C04B35/45—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on oxide ceramics based on copper oxide or solid solutions thereof with other oxides
  • C04B35/4512—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on oxide ceramics based on copper oxide or solid solutions thereof with other oxides containing thallium oxide
• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01F—COMPOUNDS OF THE METALS BERYLLIUM, MAGNESIUM, ALUMINIUM, CALCIUM, STRONTIUM, BARIUM, RADIUM, THORIUM, OR OF THE RARE-EARTH METALS
  • C01F1/00—Methods of preparing compounds of the metals beryllium, magnesium, aluminium, calcium, strontium, barium, radium, thorium, or the rare earths, in general
• • H—ELECTRICITY
  • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10N—ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10N60/00—Superconducting devices
  • H10N60/80—Constructional details
  • H10N60/85—Superconducting active materials
  • H10N60/855—Ceramic superconductors
  • H10N60/857—Ceramic superconductors comprising copper oxide

Definitions

• This invention relates to novel Tl-Ba-Ca-Cu-0 compositions which are superconducting.
• the superconducting phase has been identified as the composition La 1 _ ⁇ (Ba,S ,Ca) x Cu0 4 _ y with the tetragonal K 2 NiF 4 -type structure and with x typically about 0.15 and y indicating oxygen vacancies.
• u et al., Phys. Rev. Lett. 58, 908 (1987) disclose a superconducting phase in the Y-Ba-Cu-O system with a superconducting transition temperature of about 90 K.
• This mixture was heated in air at 925°C for more than 24 hours with several intermediate grindings to obtain a uniform black oxide Ba-Cu oxide powder which was mixed with an appropriate amount of Tl 2 0 3 , completely ground and pressed into a pellet with a diameter of 7 mm and a thickness of 1-2 mm.
• the pellet was then put into a tube furnace which had been heated to 880-910°C and was heated for 2-5 minutes in flowing oxygen. As soon as it had slightly melted, the sample was taken from the furnace and quenched in air to room temperature. It was noted by visual inspection that T1 2 0 3 had partially volatilized as black smoke, part had become a light yellow liquid, and part had reacted with Ba-Cu oxide forming a black, partially melted, porous material.
• Torardi et al.. Science 240, 631 (1988) disclose the preparation of Tl 2 Ba 2 Ca 2 Cu 3 O ⁇ 0 with an onset of superconductivity of 125 K.
• This invention provides novel superconducting compositions having the nominal formula TlBaaCa. _ Cuc0>. wherein a is from about 2 to about 4, b is from about 7/2 to about 5, c is from about 9/2 to about 7 and x ⁇ (a + b + c + y) where y is from about 1/2 to about 3.
• a is from about 2 to about 3, b is about 4, c is about 5, and y is from about 1/2 to about 2.
• the onset of superconductivity for these compositions is at a temperature of at least 130 K.
• These superconducting compositions can be prepared by heating a mixture of the oxides of Tl, Ca and Cu and the peroxide of Ba or a precursor oxide mixture prepared from these oxides, the relative amounts of the oxides chosen so that the atomic ratio Tl:Ba:Ca:Cu is l:a:b:c, to a temperature of about 940°C to about 980°C, maintaining that temperature for about 5 minutes or more, said heating being carried out in a controlled atmosphere, e. g., in a sealed tube made of a non-reacting metal such as gold, which prevents any of the reactants including the metals and oxygen from escaping.
• a controlled atmosphere e. g., in a sealed tube made of a non-reacting metal such as gold, which prevents any of the reactants including the metals and oxygen from escaping.
• FIG. 1 shows a plot of the flux excluded by a composition of this invention as a function of temperature.
• the superconducting compositions of this invention can be prepared by the following process.
• a is about 2 to about 4
• b is from about 7/2 to about 5
• c is from about 9/2 to about 7
• x (a + b + c + y) where y is from about 1/2 to about 3.
• a is about 2 to about 4
• b is from about 7/2 to about 5
• c is from about 9/2 to about 7
• x (a + b + c + y) where y is from about 1/2 to about 3.
• a is about 2 to about 4
• b is from about 7/2 to about 5
• the oxide mixture can be prepared directly by choosing quantities of the oxide reactants Tl 2 0 3 , CaO and CuO and the peroxide Ba0 2 such that the atomic ratio Tl:Ba:Ca:Cu is l:a:b:c and mixing them, for example, by grinding them together in a mortar.
• a precursor oxide mixture can be prepared by choosing quantities of the oxide reactants Tl 2 0 3 , CaO and CuO and the peroxide Ba0 2 such that the atomic ratio
• Tl:Ba:Ca:Cu is l:a:b:c.
• the barium peroxide, calcium oxide and copper oxide are ground together and this grey mixture is then heated in an alumina crucible in a muffle furnace in air, the temperature being increased from ambient temperature, about 20°C, to about 800°C in a period of about 2 hours. The temperature is held at about 800 ⁇ C for 1 hour.
• the sample is then cooled and the black powder is recovered. This powder is re-ground and ground together with the thallium oxide to give the precursor oxide mixture.
• the oxide mixture is then heated in a controlled atmosphere.
• a controlled atmosphere is to place the oxide mixture in a tube made of a non-reacting metal such as gold and then sealing the tube by crimping or, preferably, by welding or fusing.
• the precursor oxide mixture is less destructive of the gold tubes and is preferred for this reason.
• the sealed tube is placed in a furnace and heated to a temperature of about 940°C to about 980 ⁇ C and maintained at a temperature in this range, i. e., about 940°C to about 980°C, for about 5 minutes or more.
• Maintaining the sample at such a temperature for 5 minutes is sufficient to form the superconductor of the invention when the sample is heated from 700°C to a temperature in the prescribed range at a rate of 50 ⁇ C/min and subsequently cooled at a rate of 10°C/min to 600°C.
• Faster heating and cooling rates may require somewhat longer maintenance times. Maintenance times of up to an hour or more can be used but corrosion of the gold tube becomes evident at about that time and maintenance times of about 5 to about 60 minutes are typical.
• the sample is then cooled to ambient temperature and the shiny grey-black metallic-appearing ingot recovered. During the thermal cycle the gold tube typically bloats; however, at the end of the procedure there is not excess pressure in the tube when it is cut open.
• the recovered material is a shiny grey/black metallic ingot with a surface bejeweled with black shiny platelets.
• the black shiny platelets have proven to be single crystals of known materials, e. g., Tl-Ba-Ca-Cu compositions with Tl:Ba:Ca:Cu atomic ratios of 1:2:1:2 and 1:2:2:3 with lesser Tc 's.
• Resistivity measurements on the as prepared ingot shows onset at about 135 K and zero resistance at about 116 K.
• the superconductivity arises from the bulk of the composition. Based on flux exclusion measurements at least 30% of each of the samples is superconducting.
• X-ray powder diffraction typically gives very weak lines. Longer maintenance times at the maximum heating temperature have produced samples which show discrete x-ray lines.
• the 22 A (2.2 nm) c axis which is observed in the powder diffraction pattern is what is calculated for a 1245 (Tl:Ba:Ca:Cu atomic ratio) phase using a formula of Ihara et al. , Nature 334, 510 (1988). Electron microscopy results have shown intergrowth of layered phases including a 1245 phase.
• Superconductivity can be confirmed by observing magnetic flux exclusion, i.e., the Meissner effect. This effect can be measured by the method described in an article by E. Polturak and B. Fisher in Physical Review B, 36, 5586(1987).
• the superconducting compositions of this invention can be used to conduct current extremely efficiently or to provide a magnetic field for magnetic imaging for medical purposes.
• T superconducting transition temperature
• the wire mentioned previously could be wound to form a coil which would be cooled to a temperature below the superconducting transition temperature before inducing any current into the coil.
• Such fields can be used to levitate objects as large as rail ⁇ road cars.
• These superconducting compositions are also useful in Josephson devices such as SQUIDS (superconducting quantum interference devices) and in instruments that are based on the Josephson effect such as high speed sampling circuits and voltage standards.
• Flux exclusion measurements showed the onset of superconductivity at about 130 K.
• Example 2 0.456 g of Tl 2 0 3 , 1.020 g of Ba0 2 , 0.448 g of CaO and 0.960 g of CuO, corresponding to a Tl:Ba:Ca:Cu atomic ratio of
• Flux exclusion measurements showed the onset of superconductivity at about 130 K.
• Examples 3 and 4 were carried out essentially as described for Example 2 except that in Example 3, 0.456 g of Tl 2 0 3 , 0.680 g of Ba0 2 , 0.448 g of CaO and 0.960 g of CuO, corresponding to a Tl:Ba:Ca:Cu atomic ratio of 1:2:4:6, were ground to form a fine grey powder and in Example 4, 0.456 g of Tl 2 0 3 , 1.020 g of Ba0 2 , 0.448 g of CaO and 0.800 g of CuO, corresponding to a Tl:Ba:Ca:Cu atomic ratio of 1:3:4:5, were ground together to form a fine grey powder. Flux exclusion measurements showed the onset of superconductivity at about 130 K for Example 3 and at about 132 K for Example 4.
• a precursor oxide mixture was prepared by grinding together 5.10 g of Ba0 2 , 2.25 g of CaO and 4.00 g of CuO. This grey mixture was then heated in an alumina crucible in a muffle furnace in air from ambient temperature, about 20°C, to 800°C in a period of 2 hours. The temperature was held at 800°C for 1 hour and then reduced to ambient. The black powder product was recovered and re-ground. The powder contained the elements Ba:Ca:Cu in the atomic ratio 3:4:5. 2.30 g of this black powder was ground together with 0.456 g of Tl 2 0 3 to give a material with the atomic ratio of Tl:Ba:Ca:Cu of 1:3:4:5. This powder was loaded into gold tube, about 3 inches long and 1/4 inch in diameter (7.6 cm long and 0.64 cm in diameter). The tube was sealed at both ends by fusing and placed on an alumina boat which was placed in a horizontal quartz tube furnace.
• Heating was carried in the following manner. The temperature was increased from room temperature to 700°C at a rate of about 3°C/min. The temperature was then increased from 700°C to 977°C at a rate of about 18.5°C/min. The sample cooled to 950°C over the next 5 minutes and was maintained at 950°C for 10 min. The sample was then cooled in the furnace to 600°C at a rate of about 10°C/min. The sample was then removed from the furnace and cooled to room temperature. The recovered material is a shiny grey-black metallic ingot with a surface bejeweled with black shiny platelets.
• Flux exclusion measurements showed the onset of superconductivity at about 132 K.
• a precursor oxide mixture was prepared by grinding together 1.020 g of Ba0 2 , 0.448 g of CaO and 0.800 g of CuO. This grey mixture was then heated in an alumina crucible in a muffle furnace in air from ambient temperature, about 20°C, to 800°C in a period of 2 hours. The temperature was held at 800 ⁇ C for 1 hour and then reduced to ambient. The black powder product was recovered and re-ground. The powder contained the elements Ba:Ca:Cu in the atomic ratio 3:4:5.
• this black powder was ground together with 0.342 g of Tl 2 0 3 to give a material with the atomic ratio of Tl:Ba:Ca:Cu of 0.75:3:4:5 which, rounded off to integers, is approximately 1:4:5:7.
• This powder was loaded into gold tube, about 3 inches long and 1/4 inch in diameter (7.6 cm long and 0.64 cm in diameter). The tube was sealed at both ends by fusing and placed on an alumina boat which was placed in a horizontal quartz tube furnace.
• Heating was carried in the following manner. The temperature was increased from room temperature to 700°C at a rate of about 3 ⁇ C/min. The temperature was then increased from 700°C to 968°C at a rate of about 25°C/min. The sample was maintained at 968°C for 15 min. The sample was then cooled in the furnace to 600 ⁇ C at a rate of about 10 ⁇ C/min. The sample was then removed from the furnace and cooled to room temperature.
• the recovered material is a shiny grey-black metallic ingot with a surface bejeweled with black shiny platelets.
• Flux exclusion measurements showed the onset of superconductivity at about 130 K.
• Heating was carried in the following manner. The temperature was increased from room temperature to 700°C at a rate of about 3°C/min. The temperature was then increased from 700°C to 977°C at a rate of about 25°C/min. The sample was maintained at 977°C for 15 min. The sample was then cooled in the furnace to 600°C at a rate of about 10°C/min. The sample was then removed from the furnace and cooled to room temperature.
• the recovered material is a shiny grey-black metallic ingot with a surface bejeweled with black shiny platelets.
• X-ray diffraction was carried out on a powder obtained by grinding one of these products.
• the d-spacings, the relative intensities and the indices of a set of observed reflections of the X-ray powder diffraction pattern which are always present when onset of superconductivity is observed at a temperature of 130 K or above is shown in Table I.
• a precursor oxide mixture containing the elements Tl:Ba:Ca:Cu in the atomic ratio of 1:3:4:5 was prepared, placed in a gold tube and then placed in a furnace essentially as described in Example 5. Heating was carried in the following manner. The temperature was increased from room temperature to 700°C at a rate of about 3 ⁇ C/min. The temperature was then increased from 700°C to a maximum ⁇ temperature, T , at a specified rate. The sample was maintained at T for a specified time and was then cooled in the furnace to 600°C at a rate of 10°C/min except for Example 12 for which the rate was 50°C/min. The sample was then removed from the furnace and cooled to room temperature.
• the recovered material is a shiny grey-black metallic ingot with a surface bejeweled with black shiny platelets.

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• 1989
  • 1989-10-16 EP EP19900903287 patent/EP0441903A4/en not_active Withdrawn
  • 1989-10-16 AU AU50969/90A patent/AU5096990A/en not_active Abandoned
  • 1989-10-16 KR KR1019900701396A patent/KR900701659A/ko not_active Application Discontinuation
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  • 1989-10-16 JP JP90503500A patent/JPH04501553A/ja active Pending
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• 1991
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